Polybrominated diphenyl ethers (PBDEs) are man-made flame-retardant chemicals added to plastics, foams, and used in a variety of consumer products to make them difficult to burn. PBDEs exist as mixtures of similar chemicals called congeners. Because they are mixed into plastics and foams rather than bound to them, PBDEs can leave the products that contain them and enter the environment. The earliest flame retardants used in mattresses, Polychlorinated biphenyls (PCBs), are man-made organic chemicals consisting of carbon, hydrogen and chlorine atoms. They were banned in the United States in 1977 after studies revealed the wide range of toxicity and dangers to human health and environment. PCBs can remain for long periods cycling between air, water and soil and can be carried long distances far from where they were released into the environment.
References:
Polychlorinated Biphenyls (PCBs) https://www.epa.gov/pcbs/learn-about-polychlorinated-biphenyls-pcbs

Agency for Toxic Substances and Disease Registry (ATSDR). 2004. Toxicological Profile for Polybrominated Biphenyls and Polybrominated Diphenyl Ethers. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service.